RU2765561C1 - Method for casting ring castings from aluminum or magnesium alloys - Google Patents

Abstract

FIELD: foundry production.

SUBSTANCE: invention relates to the field of foundry production of aluminum and magnesium alloys, in particular to the production of castings by centrifugal casting, and can be used for the manufacture of large-sized ring castings. A method for producing ring castings from aluminum or magnesium alloys, including putting the alloy into a rotating mold, deformation treatment of castings and annealing of the resulting ring castings. The melt is fed into a rotating mold using an autonomous stationary metal dispenser located coaxially with it, consisting of a receiving bowl and a riser connected to it, having hollow nozzles at the end, each of which has a length equal to 0.7-0.95 of the inner radius of the resulting casting, and a conical channel shape tapering to the output end at an angle of α = 45-60°. In the second embodiment of the method, the melt is fed into a rotating mold using an autonomous stationary metal dispenser located coaxially with it, consisting of a receiving bowl and a riser connected to it, having at the end a horizontal disk with internal through channels whose diameter is 0.7-0.95 of the inner diameter of the resulting casting, while the channels are made with a radius of 0.25-0.45 of the inner radius of the resulting casting. Annular castings with an adjustable structure, homogeneous and fine grain in cross section are obtained.

EFFECT: low anisotropy of the mechanical properties of the semi-finished product after rolling is achieved, as well as an increase in the metal utilization factor due to a reduction in machining tolerances.

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Description

The invention relates to the field of foundry production of aluminum and magnesium alloys, in particular, to the production of castings by centrifugal casting, and can be used in mechanical engineering, rocket science and aircraft manufacturing for the manufacture of large-sized annular castings, mainly thick-walled ones, into a mold with a vertical axis of rotation.

A well-known design of a metal receiver for centrifugal casting, which has a receiving cavity and a vertical channel, turning into a horizontal channel along the radius. The vertical channel is made in the form of a packing of a confuser or conoidal type with a taper angle of the nozzle of not more than 30°, the ratio of the channel radius to the channel diameter is at least 2.0 (RF Patent No. 2402403). This design option is not applicable to casting aluminum alloys, because. it is very difficult to provide an inner lining at the point of transition along the radius of the vertical channel to the horizontal one. In addition, for alloys of other systems (steel, copper, etc.), a lining is not needed.

A known method of casting with the supply of alloy (steel) on a rotating element in the mold and spraying the metal last. With this casting method, the drops solidify on the inner surface of the rotating mold (US Patent, No. 6797081, 2004). In the proposed version, this method of casting will lead to strong oxidation of the alloy and high porosity of the casting.

Known devices for pouring metal into a rotating mold having a central riser with a conical divider installed in the center (and without it) and gating passages (radial or in the form of a segment of a ring) with casting molds attached to them using feeders (RF Patent No. 2043826, 1995 ; Inventory certificate of the USSR No. 1675038, BI No. 33, 1991 and Inventory certificate of the USSR No. 1650338, BI No. 19, 1991). Here we are talking about small shaped castings located in sand molds and having a common vertical channel for supplying metal.

As a prototype, a method for producing large-sized annular semi-finished products from wrought aluminum alloys by centrifugal casting in an inert gas environment was chosen. According to the invention, the melt is fed into the mold with the maximum possible flow rate per second, equal to 1-4% per second at the beginning of casting and 0.02-0.08% per second at the end of casting of the total mass of the casting with a gradual decrease in flow rate inversely proportional to the casting time, and the mold rotation speed is smoothly increased by 0.4-6.0% per minute from the initial speed, followed by deformation processing of the casting by rolling (RF Patent No. 2487776, V22D 13/02, 2013)

The disadvantages of this method of casting is the resulting extremely inhomogeneous structure of the casting and large allowances for machining (turning) of the workpiece.

In addition, when the melt is fed into the mold with a concentrated jet, it is torn on a rotating substrate into chaotic clots and drops, and the description of the method itself has several vague formulations:

- a distinctive feature: "... melted with a flow rate of ... 0.02-0.08% per second at the end of casting" is not localized in time. More precisely, it is necessary to talk about the solidification time of the casting, and not about the casting time;

- the action "gradually reduce the flow rate inversely proportional to the casting time" is not specifically defined;

- there is no clear expression of the parameter "initial mold rotation speed";

- the range of values of the initial speed is not indicated.

The technical objective of the present invention is to improve the quality of the casting by reducing the oxidation of the melt during centrifugal casting. To achieve this goal, the melt is fed into a rotating mold using a stationary stand-alone (fixed) dispenser-metal receiver located coaxially with the mold on the chamber cover. The dispenser consists of a receiving bowl, a riser connected to it, at the end of which there are nozzles that bring jets as close as possible to the inner surface of the annular casting.

Metal consumption (casting speed) is determined by the diameter of the channels in the nozzles, the number of the latter and the height of the melt column in the metal receiver. The metal receiver is installed with the possibility of vertical movement. The main requirement for changing the vertical position of the liquid column and the metal receiver itself: the outflowing jet must fall on the inner surface of the mold within the height of the latter.

The proposed version of the casting method significantly reduces the spattering of the jet upon impact at the beginning of casting on the surface of the mold and then on the layer of liquid metal.

To obtain the effect of casting grain refinement, it is recommended to simultaneously introduce modifier metals into the alloy: Nb, Ti, W, Ta, V, 0.01-0.05% each. The joint introduction of these metals grinds the casting grain much more than the total amount of one of them, for example:

0.02Nb+0.02Ti+0.02W+0.02Ta+0.02V.

As other methods of structure refinement, for example, continuous modification with AlTiB, AlTiC wire alloy can be used.

Instead of nozzles, you can use a collapsible disk with channels made of low-heat-conducting ceramics, which consists of two halves, and horizontal channels are made in the bottom for a tangential jet exit. The channel radius is 0.25-0.45 R, where R is the inner radius of the annular casting. This design provides a "soft" jet supply to the surface (mould) of the casting and thereby eliminates (at least sharply reduces) metal spatter, increasing the quality of the casting.

The design of the proposed dispenser-metal receiver with a disk has a simpler appearance than the design with a branch pipe, especially in relation to the mandatory lining. The dispenser is mounted on the chamber of the injection molding machine, and its lower part is located at a certain height relative to the bottom of the mold. Argon is supplied not from below through a hollow drive shaft, but from above through a coaxially located pipe around the vertical riser of the metal receiver, which greatly simplifies the operation of the entire system.

The metal consumption is regulated by changing the height of the liquid alloy column in the dispenser, as well as by means of solenoid coils put on the nozzles by applying low voltage electric current to them.

The motion of the particles of the jet flowing from the nozzle is a parabola and is determined by the equation:

where y is the coordinate of movement in the vertical direction;

x is the coordinate of movement in the horizontal direction;

g - free fall acceleration equal to 9.8 m/s;

V _o - the speed of the jet.

The velocity of the jet V _o is calculated by the formula:

where ϕ is the outflow coefficient equal to 0.82 for cylindrical nozzles and 0.96 for conical converging nozzles;

g - free fall acceleration equal to 9.8 m/s;

H is the height of the liquid column, m.

Thus, the equation of motion of the jet particles takes the following form:

where y is the coordinate of movement in the vertical direction;

x is the coordinate of movement in the horizontal direction;

H is the height of the liquid column, m.

The jet flight range is calculated by the formula:

The deviation of the vertical component of motion y (cm) is calculated depending on the height of the liquid column H (m) for specific values of X (m), i.e. from the thickness of the ring casting: 0.25; 0.3; 0.35; 0.4 m (Fig. 1 and Fig. 2).

The practical application of the above calculations can be shown in the following example shown in FIG. 3, namely: from the cup-dispenser 1 along the metal receiver 2 into the mold 3, having a size of ∅ 1200×600 mm, a billet 300 mm thick is cast. The height of the liquid column is defined as H = 0.4 m, the parameter y is equal to y = 8.37 cm. Therefore, jet 2 will fall on the wall of the mold to a point 8.37 cm away from the center line of the nozzle.

Thus, based on the calculated values of the height of the mold, a riser is placed, and by changing the height of the column H, the flight range of the jet in the process of solidification (formation) of the casting is regulated.

Metal consumption Q is determined by the formula:

where μ is the flow rate;

F is the cross-sectional area of the hole;

g - free fall acceleration equal to 9.8 m/s;

H is the height of the liquid column, m.

For most cases of water outflow from round holes (at d>10 mm) approximately μ=0.6-0.62.

при

More accurately:

at

Experiments were carried out to determine the actual values of the metal consumption Q, the range of the jet outflow x and the vertical displacement of the jet Y depending on the hydrostatic head H in relation to a real casting with a size of ∅ 1200 × 700 mm (layer thickness x=250 mm) and a mold with a height of 250 mm .

The nozzle channel diameter d was calculated, providing a flow rate of 10 kg/s at a column height of H=0.49 m (the indication was taken for ease of calculation).

from here

Accordingly, with two nozzles, the flow rate will be ~ 20 kg / s, and the diameter of the vertical part of the metal receiver will be equal to:

The expanded part of the metal receiver (dispenser) is manufactured with a height of 200 mm. It is desirable to direct the jet flowing from the channel (pipe) to the mold wall not at a right angle (perpendicular), but tangentially, for which the nozzle must be oriented in space at a certain angle, taken, for example, from the ratio R/r, where R is the inner radius of the casting , r - channel turning radius. However, in practice this is quite difficult to do, since the nozzles need to be lined from the inside, so a disk-shaped design with internal channels of any shape in cross section can be an alternative (Fig. 4).

In the analog device (RF patent No. 2402403), the vertical channel passes into the horizontal one along the radius R, the ratio of which to the diameter of the horizontal channel r is R/r ≥ 2. In the proposed case, we are talking about the configuration of the horizontal channel. Here the angle of meeting of the jet with the liquid surface layer of the casting (initially with the mold) (α) is important. The greater α, the shorter the flight range of the metal jet, the lower the pressure H. With a decrease in α, there will be less spatter, a weaker effect on the hardening crust and, consequently, less unevenness of the casting. The optimal angle of the jet meeting with the liquid surface layer of the casting is an angle of 45 - 60 degrees.

Implementation example

Mold size ∅ 1200×700 mm, height 250 mm, alloy AMg6. Casting parameters: temperature 760-780°C, rotation speed (rpm) and metal consumption (casting speed) are the same as in the selected prototype, casting in argon.

Stationary metal receiver with a height (metal column) of 0.4 m, the inner diameter of the receiving part is 100 mm, two nozzles with a length (from the axis of rotation) 280 mm, a channel diameter of 15 mm. The melt flowing out of the nozzles fell on the surface of the mold at a distance of 1/2 - 1/3 of its height from the bottom (by calculation).

The initial rotation speed of the mold was 200 rpm for ~ 5 s, then the rotation speed was gradually increased over 3 minutes to a speed of 350 rpm; the initial consumption of metal is 40-45 kg/s for 2 s and a gradual decrease in consumption by the end of casting to 20-25 kg/s for 5 minutes.

The ring blank was turned to the required dimensions. Under a small increase (multiplicity - x4), the turned inner and outer surfaces of the casting (in diameter) were visually examined for defects in the form of coarse oxide films.

Next, the casting was rolled out to ∅ 2100 × 1800 mm, then samples were cut out of it for testing mechanical properties in the shared direction (according to factory requirements).

The quality of the rolled ring was controlled for the presence of delaminations (the length of the strokes and their number on the area of the outer and inner surface of the ring).

The results of the control showed that in the cast state:

- the grain size and different-grain thickness of the casting is approximately the same in the case of casting according to the mode of the prototype, and according to the proposed method;

- on the prototype, there are noticeably more oxide inclusions on the outer surface, so it has a larger allowance for machining;

- on the rolled rings in the case of the prototype, there are delaminations from 5 to 10 mm long (strokes) in the amount of 54 pcs. on two surfaces (in total). In the ring made according to the proposed method, there are fewer bundles (the length of the strokes is from 1 to 6 mm, their number is 33 pieces).

- mechanical properties in both cases are approximately the same (in the shared direction):

δ ≈ 17%;

- in the casting mode (and design) according to the prototype, the metal is more contaminated with oxide films.

Claims (5)

1. A method for producing ring blanks from aluminum or magnesium alloys, including casting an alloy into a rotating mold, deformation processing of castings and annealing of the resulting ring blanks, characterized in that the melt is fed into a rotating mold using an autonomous fixed metal receiver located coaxially with it, consisting from the receiving bowl and the riser connected to it, having hollow pipes at the end, each of which has a length equal to 0.7-0.95 of the value of the inner radius of the resulting casting, and a conical channel shape, tapering towards the outlet end at an angle α=45 -60°. 2. The method according to p. 1, characterized in that the inert gas is fed into the mold through a coaxially located pipe around the riser of the dispenser-metal receiver. 3. The method according to p. 1, characterized in that each branch pipe is equipped with a solenoid coil, which is supplied with an adjustable electrical voltage. 4. A method for producing annular blanks from aluminum or magnesium alloys, including casting an alloy into a rotating mold, deformation processing of castings and annealing of the obtained annular blanks, characterized in that the melt is fed into a rotating mold with the help of an autonomous fixed batcher-metal receiver located coaxially with it, consisting from the receiving bowl and the riser connected to it, having at the end a horizontal disk with internal through channels, the diameter of which is equal to 0.7-0.95 from the value of the inner diameter of the resulting casting, while the channels are made with a radius of 0.25-0.45 from inner radius of the resulting casting. 5. The method according to claim 4, characterized in that an inert gas is fed into the mold through a coaxially located pipe around the riser of the metal-receiving dispenser.

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